The present invention relates broadly to the field of electronic components or devices that exhibit a positive temperature coefficient of resistivity, commonly referred to as "PTC" devices. More specifically, the present invention relates to a polymeric PTC device that is especially configured for the protection of batteries from excessive charging or draining currents.
Laminated polymeric electronic components, comprising a layer of polymeric material laminated between upper and lower metal foil layers, are well-known in the art. See, for example, U.S. Pat. No. 4,426,633--Taylor; U.S. Pat. No. 5,089,801--Chan et al.; U.S. Pat. No. 4,937,551--Plasko; and U.S. Pat. No. 4,787,135--Nagahori; U.S. Pat. No. 5,802,709--Hogge et al.; and International Publication No. WO97/06660. In such devices, the foil layers typically form electrodes, to which electrical contacts or leads are attached.
A class of polymeric electronic component that has become increasingly popular is that which employs a polymer that exhibits PTC characteristics. A particular application for polymer PTC components is in battery protection devices. In such devices, excessive charging or draining currents cause the polymer PTC material to increase in temperature to above the "switching temperature", at which its resistance increases sharply, so as to inhibit the current flow, thereby protecting the battery from damage.
Many types of electronic equipment are powered by dry cells of the AA or AAA type. It would be advantageous to provide a battery protection device that is specifically configured for use with such cells. Specifically, such a device would allow the cells to be efficiently packaged within the equipment, and would provide weldable contacts for the battery terminals.